Conventionally, an ink jet printer has been known, in which ink droplets are ejected from an ejecting head onto recording paper to print an image on the recording paper (see Japanese Laid-Open Patent Application Publication No. 2007-30370, for example). In this ink jet printer, ink is supplied through an ink supply tube from a main tank of a cartridge type to a sub-tank provided integrally with the ejecting head, and is supplied appropriately from the sub-tank to the ejecting head.
In the above described conventional ink jet printer, if air exists in the ink supply tube, ink ejecting failure of the ejecting head is likely to occur. In order to inhibit the air from being suctioned into the ink supply tube, an alarm inducing ink change is output a little time before the ink inside the main tank has been consumed and the main tank becomes empty. This brings about waste ink. It is therefore desirable to consume the whole ink inside the main tank and to discharge the air existing in the ink supply tube so as not to reach the ejecting head. To this end, a suction pump applies a negative pressure to an air layer inside the sub-tank to discharge the air so that the air existing in the ink supply tube is guided together with the ink to the sub-tank and is separated from the ink therein. Thus, the air can be discharged to outside.
However, when the suction pump applies the negative pressure to the air layer inside the sub-tank in a case where a liquid level of the ink inside the sub-tank is high, the liquid level of the ink inside the sub-tank may immediately reach an upper limit because the ink is suctioned together with the air by the suction pump, and the suction pump may stop suctioning in the state where the air still remains within the ink supply tube.